This invention is in the field of lyotropic liquid crystal (LLC) polymers, in particular cross-linked LLC copolymers having ordered nanometer-sized pores lined with functional groups. The copolymers are formed by copolymerizing LLC monomers with strong LLC character and functionalized monomers with no or weak LLC character to form an LLC phase. Both monomers contain hydrogen-bonding groups, and hydrogen-bonding is believed to assist in the formation of the LLC phase of the blended mixture.
LLC mesogens are amphiphilic molecules containing one or more hydrophobic organic tails and a hydrophilic headgroup. The amphiphilic character of these molecules encourages them to self-organize into aggregate structures in solution at sufficiently high amphiphile concentration. These aggregates can be relatively simple individual structures such as micelles and vesicles. These aggregates can also be ordered yet fluid condensed assemblies with specific nanometer-scale geometries known collectively as LLC phases. LLC phases include the normal hexagonal phase, the lamellar phase, the bicontinuous cubic phase, and the inverted hexagonal phase. FIG. 1 illustrates these phases for LLC mesogens with hydrophilic headgroups and hydrophobic organic tails in water. As shown in FIG. 1, the normal hexagonal (HI) phase has rod-like micelles arranged in a hexagonal array. The surface of the rod-like micelles is composed of the hydrophilic head groups, while the hydrophobic tails are isolated inside the micelle. The lamellar phase (L)(bilayer) phase has a double layer of molecules arranged so that the headgroups form the surface of the layer while the hydrophobic tails are isolated inside the layer. In the inverted hexagonal (HII) phase, water-filled cylindrical channels are arranged in a hexagonal array. The hydrophilic headgroups surround the channels of water while the hydrophobic tails fill the volume between the channels of water. In the bicontinuous cubic phase, channels of water are connected as a three-dimensional network. The hydrophilic headgroups surround the channels of water.
Nanostructured porous solid materials with catalytic or other functional properties are extremely important in the areas of heterogeneous catalysis, separations, and molecular sorption. The majority of the nanostructured solids used in these applications are based on zeolites and molecular sieves, which are crystalline inorganic materials which can have poor tunability and processibility. For example, there has been recent work in making organic acid-functionalized mesoporous sieve materials based on a nanostructured inorganic silicate matrix, with the strong organic acid groups chemically grafted into the nanochannels (Stein, A.; Melde, B. J.; Schroden, R. C., Adv. Mater. 2000, 12 (19), 1403-1419). Although these materials exhibit catalytic activity and have ordered nanochannels, they can suffer from processing and alignment problems since they are brittle and inorganic in nature.
A small number of reports of nanostructured polymers with nanopores containing carboxylic acid groups (COOH) have been reported. Liu et al. reported the ability to make ordered polymers with hexagonal nanochannels (ca. 17 nm I.D.) containing COOH groups via cross-linking and selectively hydrolyzing phase-separated block copolymers (Liu, G.; Ding, D., Adv. Mater. 1998, 10, 69.)
The use of cross-linked lyotropic (i.e., amphiphilic) liquid crystal (LC) phases as tunable organic zeolite and molecular sieve “analogues” for heterogeneous catalysis has been proposed. (Gin, D. L.; Gu, W. Adv. Mater. 2001, 13 (18), 1407-1410.) Lyotropic LC networks capable of enhanced heterogeneous base and Lewis acid catalysis have been designed. These LLC networks were based on polymerization of single functional monomers, rather than co-polymerization of mixtures of differing monomers. (Miller, S. A.; Kim, E.; Gray, D. H.; Gin, D. L. Angew. Chem. Int Ed. 1999, 38 (20), 3021-3026; Gu, W.; Zhou, W.-J.; Gin, D. L., Chem. Mater. 2001, 13 (6), 1949-1951.).
Formation of hydrogen-bonded LLC phases in nonpolar solution has been reported in the scientific literature. Because the solvent is nonpolar, the LLC phases are typically different than those shown in FIG. 1. Nonpolar solvents are also less likely than polar solvents to compete in hydrogen bonding between solute molecules. Gottttarelli et al. (Gottarelli, G.; Masiero, S.; Mezzina, E.; Pieraccini, S.; Spada, G. P. Liq. Cryst. 1999, 26, 965) report formation of a lyotropic crystalline phase between identical deoxyguanosine derivatives in hydrocarbon solvents. The proposed structure for the gel-like phase was a structure formed by ribbon-like elements containing guanine residues in an extended hydrogen-bonded configuration, while didacanoyl chains, together with the hydrocarbon solvent, fill the lateral gap between the ribbons. Kanie et al. (Kanie, K.; Yasuda, T.; Nishii, M.; Ujiie, S.; Kato, T. Chem. Lett. 2001, 480) report formation of ribbon-like and disk-like aggregations between identical folic acid derivatives in dodecane.
Formation of hydrogen-bonded disk-like aggregates in water between an equimolar mixture of a melamine derivative and an isocyanuric acid derivative has also been reported (Paleos, C. M.; Tsiourvas, D. Adv. Mater. 1997, 9, 695). A bi-layer structure was proposed, with each layer consisting of a hydrogen bonded array of the two molecules.
There remains a need for nanostructured organic materials with a range of architectures which can be functionalized with a broad range of functional groups.